When the Nova Horizons probe reached the dark outer reaches of the Solar System, in addition to Pluto, their instruments picked up new things.
Very faintly, the space between the stars was blazing with optical light. This was not in itself unexpected; this light is called the cosmic optical color, a faint light from all the lights in the Universe outside our galaxy.
It was a strange part of the light. Significantly more than scientists thought there should be – twice as much, in fact.
Now, in a new paper, scientists posit a possible explanation for the excess optical light: a by-product of the unobservable interaction of dark matter.
“The results of this work,” write the researchers, who were led by astrophysicist José Luis Bernal of Johns Hopkins University, “provide a potential explanation for the excess of the cosmic optical career, which is allowed by independent observational constraints, and can answer one of the most long-standing unknowns in cosmology: the nature of dark matter”.
We have many questions about the universe, but dark matter is the most troubling. We give this name to the mysterious mass in the universe It is responsible for providing far less gravity in contracted areas than it should be.
so that the galaxies rotate faster than they should under the gravity that is generated by the visible mass of matter.
The curvature of spacetime around massive objects is greater than it should be if we count the curvature of spacetime as only hot matter.
But whatever creates this effect, we cannot directly detect. The only way we know it is that we can’t just figure this out of gravity.
It is a real property. About 80 percent of the matter in the universe is dark matter.
There are some hypotheses about what might happen. One of the candidates is the axion, which belongs to a class of molecular particles first conceived in the 1970s to solve the question of why strong atomic forces follow something called charge symmetry, when most models say they don’t.
As it turns out, axions in the specific mass environment should also behave exactly as we expect dark matter to behave. And there could be a way to detect them, because theoretically, axions are expected to decay into pairs of photons in the presence of a strong magnetic field.
Some experiments are looking for sources of these photons, but they must also be streaming through space in excessive numbers.
The difficulty is to separate them from all other light sources in the universe, and this comes in a cosmic perspective.
The place itself is very difficult to detect when it is so faint. The Long Range Reconnaissance Imager (LORRI) launched on New Horizons is perhaps the best tool for the job yet. It is far from Earth and the Sun, and LORRI is far more sensitive than the Voyager probes that were launched 40 years ago.
Scientists have assumed that the excess detected by New Horizons is a product of stars and galaxies that we cannot see. And that option is still very much on the table. Bernal and his team needed to assess whether dark axion-atral events might be responsible for extra-light.
They performed mathematical modeling and determined that axions with charges between 8 and 20 electron volts could produce the observed signal under certain conditions.
It is incredibly light for a particle that is usually measured in megaelectronvolts. But with recent estimates placing the molecular fraction of matter at a fraction of one electronvolt, these numbers will require relatively massive axions.
It is impossible to tell which explanation is correct based on the present data alone. The researchers, however, in narrowing down the masses of the axes that may be excesses, have laid the foundations for future investigations of these enigmatic particles.
“If the excess arises from the decay to the dark photon line, there will be a noticeable signal in the intended measurements of the line intensity,” the researchers write.
“Furthermore, the ultraviolet instrument on New Horizons (which will have better sensitivity and explore a different range of the spectrum) and future studies of very high energy gamma-ray attenuation will also test this hypothesis and expand the search for dark matter to a wider range of frequencies.”
The research was published in Physical Review Letters.
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